1. Field of the Invention
The present invention relates to a throttle valve control apparatus which conducts so-called electronic throttle control where a throttle valve of an internal combustion engine is controlled to attain a required opening determined using additional information as well as an accelerator operation quantity instead of driver""s operating an accelerator, thereby directly controlling the throttle valve.
2. Description of the Related Art
As a conventional throttle valve control apparatus, a throttle valve control apparatus which simultaneously realizes quick response when a deviation between a required opening and an actual opening of a throttle valve is small, and convergence stability when the deviation is large is disclosed (for example, see JP 10-176579).
In the related art, a map is prepared which sets a larger value to the proportional gain and the integral gain as the deviation becomes smaller, both of the gains are temporarily determined by referring to the map for a given deviation in a transient state, the temporary gains and gains used in the previous cycle are compared, thereby selecting the smaller gains of them, and a driver signal is calculated based on the selected gains. Thus, since large gains are used when the deviation is small, proper follow-up is provided. Also, since small gains provided for a large deviation are still used for the control after the deviation becomes small, an overshoot is not generated by an excessive driving force.
Meanwhile, the related art has the following problems. There is no trouble when the throttle valve operates ideally according to the drive signal. However, when the motion of the throttle valve encounters an obstruction, such as getting stuck, while in a transient state, since the control coefficient is fixed to a control coefficient corresponding to a large deviation, namely a small control coefficient, the drive signal remains small. Consequently, the throttle valve does not operate until the integral term becomes large, and eventually it starts operating after the integral term becomes large. As a result, the response of the throttle opening becomes fairly degraded.
The present invention is devised to solve the problems described above, and provides a throttle valve control apparatus which simultaneously realizes quick response and stability even when the throttle valve gets stuck in its operation.
A throttle valve control apparatus according to the present invention includes:
a deviation calculating unit which calculates a deviation between a target opening and an actual opening of a throttle valve;
a reference unit which outputs a control coefficient for the individual deviation;
a temporarily determining unit which refers to the reference unit at a predetermined interval so as to temporarily determine a temporary control coefficient corresponding to the deviation;
a coefficient limiting unit which determines an actual control coefficient for the present period based on comparing the temporary control coefficient temporarily determined by the temporarily determining unit, with a stored actual control coefficient determined for the previous period;
a present value storing unit which stores the actual control coefficient determined by the coefficient limiting unit; and
a drive signal determining unit which determines a drive signal for the throttle valve based on the actual control coefficient obtained from the coefficient limiting unit and the deviation obtained from the deviation calculating unit,
in which the coefficient limiting unit has a permissible change predetermined for the change of the control coefficient which changes for a single period, obtains a difference as a change between the temporary control coefficient temporarily determined by the temporarily determining unit and the actual control coefficient for the previous period stored in the present value storing unit at predetermined periods, and limits the obtained change according to the permissible change so as to determine the actual control coefficient for the present period, thereby fitting the change from the actual control coefficient for the previous period to the actual control coefficient for the present period into the permissible change.